Distributed power railroad train operation supplies motive power and braking action from a lead locomotive (or lead unit) and one or more remote locomotives (or remote units) spaced apart from the lead unit in a train. In one configuration, a distributed power train comprises a lead locomotive at a head end of the train, a remote locomotive at an end of train (EOT) position and one or more mid-train locomotives disposed between the head end and the end of train. Distributed train operation may be preferable for long train consists to improve train handling and performance, and especially for trains operating over mountainous terrain.
In a distributed power train, each lead and remote locomotive supplies motive power and braking action for the train. Motive and braking command messages are issued by an operator in the lead locomotive and supplied to the remote locomotives over a radio frequency communications system, (such as the prior art LOCOTROL® distributed power communications system, available from the General Electric Company of Schenectady, New York) comprising a radio frequency link (channel) and receiving and transmitting equipment at the lead and the remote units. The receiving remote locomotives respond to these commands to apply tractive effort or braking effort to the train, and advise the lead unit of the receipt and execution of the command. The lead unit also sends other messages to the remote units, including status request messages. The remote units respond by sending a status reply message back to the lead unit.
In a train having two or more directly coupled remote locomotives, the coupled locomotives function in unison via control signals transmitted over their connected MU (multiple unit) lines. One of the locomotives is designated as a controlling remote unit with respect to the distributed power communications system. Only the controlling remote unit is configured to receive commands transmitted by the lead unit and respond to the lead unit with appropriate reply messages.
One of the most critical aspects of train operation is the predictable and successful operation of the air brake system. The air brake system comprises locomotive brakes in each locomotive (including the lead locomotive and all the remote locomotives) and car brakes at each railcar. The lead unit locomotive brakes are controlled by the locomotive operator in response to a position of a locomotive brake handle, and the rail car brakes are controlled in response to a position of an automatic brake handle. The locomotive brakes can also be controlled by the automatic brake handle.
The automatic brake handle or controller controls a pressure in a fluid carrying brake pipe that extends the length of the train and is in fluid communication with a car brake system for applying or releasing car brakes at each railcar in response to a pressure change in the brake pipe. Specifically, a control valve (typically comprising a plurality of valves and interconnecting piping) at each railcar responds to changes in the brake pipe fluid pressure by applying the brakes (in response to a decrease in the brake pipe fluid pressure) or by releasing the brakes (in response to an increase in the brake pipe fluid pressure). The fluid within the brake pipe conventionally comprises pressurized air. Operator control of the automatic brake handle in the lead locomotive initiates a pressure drop at the lead unit that propagates along the brake pipe to the end of the train. The control valve at each railcar senses the pressure drop and in response thereto supplies pressurized air from a local railcar reservoir to wheel brake cylinders that in turn draw brake shoes against railcar wheels. The railcar reservoir is recharged by air withdrawn from the brake pipe during non-braking operational intervals.
A brake release is also commanded by the lead operator by controlling the automatic brake handle to effect a pressure increase in the brake pipe. The pressure increase is sensed at the railcars and in response the brake shoes are released from the railcar wheels.
In a distributed power train, in addition to regulating the brake pipe pressure to effect application and release of the railcar brakes, the lead unit commands remote unit brake applications and releases by sending an appropriate signal to the remote units via the communications channel. As described further below, brake applications and releases are thus more rapidly affected along the length of the train due to the participation of both the lead unit and the remote units. With some limitations as required to maintain train control, in a distributed power train a brake command or brake release can also be commanded by the lead or the remote locomotives.
The railcar brakes can be applied in two modes, i.e., a service brake application or an emergency brake application. In a service brake application, braking forces are applied to the railcar to slow or bring the train to a stop at a forward location along the track. During service brake applications the brake pipe pressure is slowly reduced and the brakes are applied gradually in response thereto. The operator controls the rate at which the pressure is reduced by operation of the automatic brake control handle. A penalty brake application is one form of a service brake application in which the brake pipe is reduced to zero pressure, but the evacuation occurs at a predetermined rate, unlike an emergency brake application as described below, and the railcars do not vent the brake pipe during the penalty brake application.
An emergency brake application commands an immediate application of the railcar brakes through an immediate evacuation or venting of the brake pipe at the lead unit (and the remote units of a distributed power train). When a railcar senses a predetermined pressure reduction rate indicative of an emergency brake application, the railcar also vents the brake pipe to accelerate propagation of brake pipe evacuation along the train. Unfortunately, because the brake pipe runs for several thousand yards through the train, the emergency brake application does not occur instantaneously along the entire length of the brake pipe. Thus the braking forces are not uniformly applied at each railcar to stop the train.
On distributed power trains, braking is accomplished by venting the brake pipe at both the lead and remote locomotives, thus accelerating the brake pipe venting and application of the brakes at each railcar, especially for those railcars near the end of the train. As can be appreciated, brake pipe venting at only the lead unit in a conventional train requires propagation of the brake pipe pressure reduction along the length of the train, thus slowing brake applications at railcars distant from the lead unit. For a distributed power train with an operative communications link between the lead and remote units, when the train operator commands a brake application (e.g., a service or an emergency brake application) by operation of the automatic brake control handle at the lead unit, the brake pipe is vented and a brake application command is transmitted to each remote unit over the radio frequency communications link. In response, each remote unit also vents the brake pipe. Thus braking action at the remote locomotives follows the braking action of the lead unit in response to signals transmitted by the communications system.
A brake release initiated at the lead unit is also communicated over the radio frequency link to the remote units so that the brake pipe is recharged to a nominal pressure from all locomotives, reducing the brake pipe recharge time.
If an emergency brake application is initiated at the lead locomotive by the train operator or in response to a detected failure condition, the radio frequency communication system sends an emergency brake signal to each of the remote locomotives over the radio frequency link. In response, the remote locomotives evacuate the brake pipe. This technique permits faster execution of the emergency brake application since the brake pipe is evacuated from all of the locomotives, rather than from only the lead locomotive as in a conventional train.
FIGS. 1 and 2 schematically illustrate an exemplary distributed power train 10, traveling in a direction indicated by an arrowhead 11, wherein one or more remote units 12A-12C are controlled from either a lead unit 14 (FIG. 1) or a control tower 16 (FIG. 2). A locomotive 15 is controlled by the lead unit 14 via an MU line 17 connecting the two units. The teachings of the present invention can be applied to the distributed power train 10 and a communications system operative therewith as described below.
It should be understood that the only difference between the systems of FIGS. 1 and 2 is that the issuance of commands and messages from the lead unit 14 of FIG. 1 is replaced by the control tower 16 of FIG. 2 and certain interlocks of the system of FIG. 1 are eliminated. Typically, the control tower 16 communicates with the lead unit 14, which in turn is linked to the remote units 12A-12C.
In one embodiment, a communications channel of the communications system comprises a single half-duplex communications channel having a three kHz bandwidth, where the messages and commands comprise a serial binary data stream encoded using frequency shift keying modulation on one of four available carrier frequencies. The various bit positions convey information regarding the type of transmission (e.g., message, command, alarm), the substantive message, command or alarm, the address of the receiving unit, the address of the sending unit, conventional start and stop bits and error detection/correction bits. The details of the messages and commands provided by the system and the transmission format of individual messages and commands are discussed in detail in commonly owned U.S. Pat. No. 4,582,280, which is hereby incorporated by reference.
The distributed power train 10 of FIGS. 1 and 2, further comprises a plurality of railcars 20 interposed between the remote units 12A/12B and between the remote unit 12C (of FIG. 1). The arrangement of the locomotives 14 and 12A-12C and railcars 20 illustrated in FIGS. 1 and 2 is merely exemplary, as the present invention can be applied to other locomotive/railcar arrangements. The railcars 20 are provided with an air brake system (not shown in FIGS. 1 and 2) that applies the railcar air brakes in response to a pressure drop in a brake pipe 22, and releases the air brakes upon a pressure rise in the brake pipe 22. The brake pipe 22 runs the length of the train for conveying the air pressure changes specified by the individual air brake controls 24 in the lead unit 14 and the remote units 12A, 12B and 12C.
In certain applications, an off board repeater 26, further described below, is disposed within radio communication distance of the train 10 for relaying communications signals between the lead unit 14 and the remote units 12A, 12B and 12C.
The lead unit 14, the remote units 12A, 12B and 12C, the off board repeater 26 and the control tower 16 are provided with a transceiver 28 operative with an antenna 29 for receiving and transmitting communications signals over the communications channel.
The lead unit transceiver 28 is associated with a lead station 30 for generating and issuing commands and messages from the lead unit 14 to the remote units 12A-12C, and receiving reply messages therefrom.
Commands are generated in the lead station 30 in response to operator control of the motive power and braking controls within the lead unit 14, as described above, or automatically as required. Each remote unit 12A-12C and the off board repeater 26 comprises a remote station 32 for processing and responding to transmissions from the lead unit 14 and for issuing reply messages and commands.
The four primary types of radio transmissions carried by the communications system include: (1) link messages from the lead unit 14 to each of the remote units 12A-12C that “link” the lead unit 14 and the remote units 12A-12C, i.e., configure or set-up the communications system for use by the lead unit 14 and the remote units 12A-12C, (2) link reply messages that indicate reception and execution of the link message, (3) commands from the lead unit 14 that control one or more functions (e.g., application of motive power or braking) of one or more remote units 12A-12C and (4) status and alarm messages transmitted by the one or more remote units 12A-12C that update or provide the lead unit 14 with necessary operating information concerning the one or more remote units 12A-12C.
Each message and command sent from the lead unit 14 is broadcast to all of the remote units 12A-12C and includes a lead unit identifier for use by the remote units 12A-12C for determining that the sending lead unit is the lead unit of the same train. An affirmative determination causes the remote unit 12A-12C to execute the received command.
Messages and alarms sent from one of the remote units 12A-12C also include the sending unit's address. As a result of a previously completed link-up process, the receiving unit, i.e., the lead or another remote locomotive, can determine whether it was an intended recipient of the received transmission by checking the sending unit's identification in the message, and can respond accordingly.
These four message types, including the address information included in each, ensure a secure transmission link that has a low probability of disruption from interfering signals within radio transmission distance of the train 10. The messages allow for control of the remote units 12A-12C from the lead unit 14 and provides remote unit operating information to the lead unit 14.
Although most commands are issued by the lead unit 14 and transmitted to the remote units 12A-12C for execution as described above, there is one situation where a remote 12A-12C issues commands to the other remote units and the lead unit 14. If a remote unit 12A-12C detects a condition that warrants an emergency brake application, the remote transmits an emergency brake command to all other units of the train. The command includes identification of the lead locomotive of the train and will therefore be executed at each remote unit, as if the command had been issued by the lead unit.
Throughout the description of the present invention, the terms “radio link”, “RF link” and “RF communications” and similar terms describe a method of communicating between two links in a network. It should be understood that the communications link between nodes (locomotives) in the system in accordance with the present invention is not limited to radio or RF systems or the like and is meant to cover all techniques by which messages may be delivered from one node to another or to plural others, including without limitation, magnetic systems, acoustic systems, and optical systems. Likewise, the system of the present invention is described in connection with an embodiment in which radio (RF) links are used between nodes and in which the various components are compatible with such links; however, this description of the presently preferred embodiment is not intended to limit the invention to that particular embodiment.
In a distributed power train, responsive to an operator-initiated command, the communications system at the lead unit transmits to each remote unit a radio frequency (RF) message representing the command. Such commands can include locomotive throttle or traction commands and air brake, dynamic brake and electric brake commands. In the case of an air brake command, upon message receipt, the brake command is executed at each remote unit to accelerate command response at the railcars, since the remote units receive the radio frequency message before they sense the brake pipe pressure change. For example, if the operator commands a brake application, the brake pipe is vented at the lead unit and the pressure reduction propagates along the length of the train until reaching the end-of-train car. Depending on train length, several seconds may elapse before the pressure reduction reaches the last railcar. Venting the brake pipe at the lead and remote locomotives, the latter in response to the RF message, accelerates the brake pipe venting and application of the brakes at each railcar, especially for the railcars near the end of the train. Thus braking actions at the remote locomotives follow the braking actions of the lead unit in response to the RF signals transmitted by the communications system.
A brake release initiated at the lead unit is also communicated over the radio frequency link to the remote units so that the brake pipe is recharged to its nominal pressure from all locomotives, reducing brake pipe recharge time.
If the train operator initiates an emergency brake application at the lead locomotive, the communication system sends an emergency brake signal to each of the remote locomotives over the radio frequency link. The remote locomotives evacuate the brake pipe to provide faster execution of the emergency brake application since the brake pipe is evacuated from all of the locomotives, rather than from only the lead locomotive as in a conventional train.
In general, messages sent over the communications system permit the application of more even tractive forces to the railcars and improve braking performance as each locomotive can effect a brake application at the speed of the RF signal, rather than the slower speed at which the pneumatic brake pipe braking signal propagates along the train.
When the distributed power train is operating in an environment where each remote unit is expected to receive command messages sent by the lead unit, for example when the train is traveling along a relatively straight length of track with no proximate obstructions to a radio frequency signal, the communications system is operative in a normal mode. In this mode, no communications losses, interruptions or repeated messages (because the message did not reach its intended destination when first transmitted) are anticipated. Most messages issued in the normal mode are controlled according to a fixed priority message protocol, according to which each remote unit transmits a status message responsive to a lead-issued command message after a predetermined interval from transmission of the command. Thus each remote unit is assigned a time slot, measured from transmission of the lead unit command message, during which each remote unit transmits its message.
A timing diagram of FIG. 3, where the system is described for a railroad train comprising a lead unit and four remote units, illustrates the concepts associated with the fixed priority message protocol for normal communications. The concepts described in conjunction with FIG. 3 can be applied to a train comprising more or fewer than four remote locomotives.
According to this scheme, at a time t=650 msec, the lead unit transmits a command message (for example, a brake command, a traction command, a dynamic brake command, etc.) that is expected to be received by all remote locomotives in the distributed power train. As can be seen in FIG. 3, each transceiver (radio) is allocated a 30 msec interval to turn on, and an exemplary command message length is 193 msec. After a lapse of the predefined interval from the lead transmission, for example 50 msec as indicated in FIG. 3, a first remote locomotive retransmits the command message and its status message (for example, the first remote locomotive is venting the brake pipe in response to the brake command). The status message is intended for the lead locomotive so that the train operator is advised of the first remote unit's response to the command. Also note that each remote unit retransmits the command message with its status message to maximize the likelihood that the command is received by all remote locomotives. The turn-on time, message duration, etc. illustrated in FIG. 3 are merely exemplary and can vary depending on the application and specifications of the components that comprise the communications system.
The second remote locomotive repeats the command message and transmits its status message after a predetermined delay, for example 50 msec, from the end of the first remote's transmission. The command repeating and status transmitting process continues until all remote locomotives have repeated the command message and transmitted their respective status message. An end of message condition occurs when the last remote has transmitted its status, after which the lead unit is free to transmit another command message to the remote locomotives. In the FIG. 3 embodiment, the end of message occurs at t=2896 msec or 2271 msec after the lead unit's initial transmission.
When the lead unit transmits a command message, the lead unit will not know whether the message was received by all the remote units in the train until a remote status message is received from each remote unit (wherein the status messages indicates receipt and execution of the command message) or a status message is not received from one or more of the remote units (lack of a status message indicates the command message was not received). Thus according to one embodiment of the communications system, to ensure that each remote unit receives the command messages, it is repeated by each remote unit.
Note that it is possible that one or more remote status messages may not be received by the lead unit. When this is the case, the lead unit retransmits the command message and awaits a reply status message from each remote unit in the train. One feature of the present invention, to be described below, increases the likelihood that all status messages are received at the lead unit, thus reducing the retransmit probability, without significantly impacting the overall transmission timing for the command and status messages.
In addition to the fixed priority protocol described above, certain commands, e.g., an emergency brake application, are classified as high priority command messages and are transmitted according to a different priority protocol than the fixed priority protocol. Still other command messages, e.g., a communications system check, operate according to other priority protocols that control transmission of these commands and the reply by the remote units.
As the distributed power train passes through certain terrain topographies or track segments with proximate natural or man-made obstructions, a line-of-sight communications link between the sending and the receiving units may be interrupted. Thus commands and status messages may not be reliably received by the receiving unit, i.e., the lead locomotive for messages sent from a remote unit, and a remote locomotive for messages sent from the lead unit. Although high-power, robust transceivers may be capable of successfully transmitting the signal to the receiving unit under certain operating conditions, such equipment can be relatively expensive. Further, in some operating scenarios even a high-power transceiver cannot successfully effect communications, such as when a long train travels a curved track segment adjacent a natural obstruction such as a mountain, where the communications path between the lead unit and one or more remote units is obstructed by the mountain. Also, as the train passes through a tunnel certain transceivers may be unable to communicate with other transceivers aboard the locomotives.
To improve system reliability, one embodiment of the distributed power train communications system comprises the off-board repeater 26 (see FIG. 1) for receiving messages sent from the lead unit 14 and repeating (retransmitting) the message for receiving by the remote units 12A-12C. This embodiment may be practiced along a length of track that passes through a tunnel, for example. In such an embodiment the off-board repeater 26 comprises an antenna 29 (e.g., leaky coaxial cable mounted along the tunnel length) and the remote station 32 for receiving and retransmitting lead messages that are received by all the remote units 12A-12C within RF communications range of the repeater antenna 29.